Mounting bracket for strain sensor

ABSTRACT

The subject matter of this specification can be embodied in, among other things, a system for mounting a strain sensor on a tubular pipe, which includes a mechanical clamp. The clamp has a bottom flexing section having an arcuate portion terminating at a first terminal and at a second end, and a first and second upper flexing sections having an arcuate portions terminating at first terminal ends and at second terminal ends in a pivot pin assembly having a bore parallel to a central longitudinal axis of the clamp, the bore there through for receiving a removable connector. Sensor mounting arms are disposed outwardly on the first and second upper flexing sections, said sensor mounting arms including at least one receptacle sized to receive and retain ends of a strain gauge.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a Divisional of U.S. application Ser. No. 14/408,243filed on Dec. 15, 2014, entitled “MOUNTING BRACKET FOR STRAIN SENSOR,”currently pending; which application is a U.S. National Stage ofInternational Application No. PCT/US2013/077990, filed Dec. 27, 2013,entitled “MOUNTING BRACKET FOR STRAIN SENSOR,” both of which arecommonly assigned with the present invention and incorporated herein byreference.

TECHNICAL FIELD OF THE INVENTION

The present disclosure relates to an apparatus for mounting sensors onpipe sections.

BACKGROUND OF THE INVENTION

In connection with the recovery of hydrocarbons from the earth,wellbores are generally drilled using any of a variety of differentmethods and equipment. According to one common method, a drill bit isrotated against the subsurface formation to form the wellbore. The drillbit may be rotated in the wellbore through the rotation of a drillstring attached to the drill bit and/or by the rotary force imparted tothe drill bit by a subsurface drilling motor powered by the flow ofdrilling fluid down the drill string and through downhole motor.

The flow of drilling fluid can exhibit variations in pressure. Thesepressure variations can cause dimensional changes in solid structuressuch as piping that carries the drilling fluid to and from the drillstring. Strain gauges are used for detection and measurement of absolutedimensional changes of solid structures, such a piping for drillingfluid, but such changes are generally very slow and difficult to observewith known equipment and measurement methods.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an example optical sensor mount;

FIGS. 2 and 3 are exploded and perspective views of another exampleoptical sensor mount.

FIG. 4 is a conceptual representation of an example optical sensor mountin a stressed condition.

FIG. 5 is a conceptual representation of an example optical sensor mountin a stressed condition.

FIG. 6 is another conceptual representation of an example optical sensormount in a stressed condition.

DETAILED DESCRIPTION

This document describes systems and techniques for mounting sensorattachments to drilling fluid (also referred to in the industry asdrilling mud) piping on drilling rigs. The assemblies described in thisdocument can be used to mount several different types of opticalsensors, including temperature, pressure, and/or strain sensors. Some ofthese sensors can be optical sensors and gauges based on the operatingprinciples of a Fiber-Bragg grating and/or Fabry-Pérot interferometer.

In general, optical sensor mounts clamp, attach, or are otherwiseaffixed to an outside surface of one or more pipes in the drilling fluidpiping system. Fluid (for example, drilling fluid) flowing through thepipe exerts a pressure force outward against the pipe, which causessmall changes in the diameter of the pipe that vary with the pressure ofthe fluid within. The optical sensor mounts mechanically transfer, andin some implementations, amplify or reduce, changes in pipe diameter toone or more sensors. The signal outputs of such sensors can then beprocessed to observe changes in the diameter of the pipe. The changes indiameter of the pipe diameter may be processed using known physicalcharacteristics of pressure pipes as described, for example, in“Pressure Vessel Design Manual” by Dennis Moss. Detection of saidchanges can allow for downhole pressure pulse detection whereas saidpressure pulses can convey the specific information or data content,examples of which are described in Halliburton patents U.S. Pat. No.7,480,207B2 and U.S. Pat. No. 7,404,456 B2.

FIG. 1 is a perspective view of an example optical sensor mount 100. Themount 100 is a generally circular mechanical clamp having an innerdiameter 102 sized to accommodate an outer diameter of a pipe (notshown) on which the mount 100 is to be mounted. The mount 100 includesthree main sections, including a bottom flexing section 120, a firstupper flexing section 140, and a second upper flexing section 160.

The bottom flexing section 120 is a generally semi-circular arcuateportion, having a terminal end 122 a in a mounting wing 124 a, and aterminal end 122 b in a mounting wing 124 b. The mounting wing 124 a isformed generally perpendicular to the terminal end 122 a, and themounting wing 124 b is formed generally perpendicular to the terminalend 122 b. The mounting wing 122 a includes a bore 126 a, and themounting wing 122 b includes a bore 126 b, the bores 126 a-126 b forreceiving a removable connector (not shown) such as a bolt or otherappropriate fastener.

The bottom flexing section 120 has a thickness 128. The bottom flexingsection 120 includes a subsection 130 that has a thickness 132 that isless than the thickness 128. In some implementations, as the bottomflexing section 120 flexes, the relatively lesser thickness 132 of thesubsection 130 may cause distortion of the bottom flexing section 120 tobe at least partly concentrated along the subsection 130.

The upper flexing section 140 includes an arcuate portion 142 that isgenerally quarter-circular in shape, terminating at a terminal end 143in a mounting wing 144 and a terminal end 146 in a mounting wing 148.The mounting wing 144 is formed generally perpendicular to the terminalend 143 and includes a bore 150 for receiving a removable connector (notshown) such as a bolt or other appropriate fastener when the bore 150 isaligned with the bore 126 a to removably affix the upper flexing section140 to the bottom flexing section 120.

The mounting wing 148 is formed generally tangent to the terminal end146 and includes a pivot pin assembly 152 having a bore 153 that isformed parallel to a central longitudinal axis 103 of the mount 100. Thebore 153 is formed to receive a removable connector (not shown) such asa bolt or other appropriate fastener.

A sensor mounting arm 154 extends generally perpendicular from the upperflexing section 140. The sensor mounting arm 154 including at least onereceptacle 156 sized to receive and retain an end 192 a of a sensor 190,such as a strain gauge, an optical sensor, a Fiber-Bragg grating, aFabry-Pérot interferometer etalon, or any other appropriate sensor.

The upper flexing section 160 includes an arcuate portion 162 that isgenerally quarter-circular in shape, terminating at a terminal end 163in a mounting wing 164 and a terminal end 166 in a mounting wing 168.The mounting wing 164 is formed generally perpendicular to the terminalend 163 and includes a bore 170 for receiving a removable connector (notshown) such as a bolt or other appropriate fastener when the bore 170 isaligned with the bore 126 b to removably affix the upper flexing section160 to the bottom flexing section 120.

The mounting wing 168 is formed generally tangent to the terminal end166 and includes a pivot pin assembly 172 having a bore 174 that isformed parallel to the central longitudinal axis 103 of the mount 100.The bore 174 is formed to receive a removable connector (not shown) suchas a bolt or other appropriate fastener when aligned with the bore 153.

A sensor mounting arm 175 extends generally perpendicular from the upperflexing section 160. The sensor arm 175 including at least onereceptacle 176 sized to receive and retain an end 192 b of the sensor190.

The mount 100 includes a collection of adjustment rods 180. Theadjustment rods extend through the mount 100 inwardly in a radialdirection toward the longitudinal axis 103 of the mount 100 through acollection of adjustment openings 181. The inward end of each of theadjustment rods 180 terminates in a landing pad 182. The adjustment rods180 and the landing pads 182 form a collection of adjustment assemblies184 formed to move the adjustment rods 180 and the landing pads 182 intoadjustable contact with the pipe on which the mount 100 is to bemounted. In some embodiments, the adjustment assemblies 184 can includefemale threads in each of the adjustment openings, and the adjustmentrods 180 can include at least a portion with male threads adapted to bereceived in the female threads. In some embodiments, compression padscan be affixed to the landing pads 182. In some embodiments, thecompression pads can include layers of vibration and acoustic noiseabsorbing material.

When assembled in a substantially unstressed or a predeterminedpre-stressed or strained configuration, the sensor mounting arms 154 and175 are oriented substantially parallel to each other. In such asubstantially parallel configuration, the sensors 190 are stressed tosubstantially the same degree. For example, two sensors 190 in theexample parallel configuration can provide substantially the sameoutputs, which can be used to cancel out common mode noise differentialmeasurement configurations.

In some implementations, the mount 100 can be removably affixed to apipe by placing a fastener though the bores 126 a and 150, and byplacing another fastener through the bores 126 b and 170, while omittinga fastener from the pivot pin assemblies 152, 172. In such an exampleconfiguration, as the pipe varies in diameter (e.g., due to variationsin pressure of the fluid within the pipe), the unfastened pivot pinassemblies 152, 172 can separate slightly, causing the sensor mountingarms 154 and 175 to move away from their substantially parallel,unstressed configuration. As the sensor mounting arms 154 and 175diverge, the sensors 190 mounted at different radial positions on thesensor mounting arms 154 and 175 will experience differing amounts ofstress. In some implementations, the differing amounts of stress canproduce a differential signal by the sensors 190 that can be processedto determine the absolute or change in fluid pressure within the pipe.

Referring now to FIG. 4, a simplified version of the mount 100 is shownto illustrate one example effect of stress upon the mount 100. In theillustrated example, the upper flexing sections 140, 160 are removablyaffixed to the bottom flexing section 120 by a pair of bolts 410 and therestraining bolt (not shown here) is inserted in the bores 153, 174.When the mount 100 is clamped about a pipe (not shown) that issubstantially unpressurized and therefore substantially unexpanded, themount 100 can take on the configuration shown in solid lines. When thepipe is pressurized, the walls of the pipe will expand. This expansionwill cause the sensor mount arms 154 and 175 to converge or otherwisemove relatively closer, taking on the configuration shown in dottedlines.

Referring again to FIG. 1, in some implementations, a linking plate 195can be removably affixed to the radially distal ends of the sensormounting arms 154 and 175 with respect to each other, mechanicallylinking the sensor mounting arms 154 and 175 to each other. By linkingthe sensor mounting arms 154 and 175 to each other through the linkingplate 195, the movement of the sensor mounting arms 154 and 175 as thepipe expands and contracts can be modified. In some implementations, thelinking plate 195 may be used as an aid to assembly of the mount 100about the pipe. For example, the linking plate 195 may be used totemporarily affix the upper flexing sections 140, 160 during assembly,and may be removed after the upper flexing sections 140, 160 are affixedto the bottom flexing section 120.

Referring now to FIGS. 5 and 6, simplified versions of the mount 100 areshown to illustrate the effects of the linking plate 195 on the flexureof the mount 100. FIG. 5 is a conceptual example configuration 500 ofthe mount 100 without the linking plate 195 and without the restrainingbolt. In the example configuration 500, as the pipe (not shown) expandswithin the mount 100, the sensor mounting arms 154 and 175 move fromtheir substantially unstressed or pre-stressed configuration, asdepicted in dotted lines, relatively apart to the stressed configurationdepicted in solid lines. In general, without the linking plate 195 inplace, the radially distal ends 510 of the sensor arms 154 and 175 willmove relatively further apart from each other than will more radiallyproximal portions 520 of the sensor arms 154 and 175.

In some implementations, as the pressurized pipe's diameter D increasesby X, the strain can be expressed as a ratio X/D. The same displacementX applied over a shorter distance L between expansion arms can lead tostrain amplification because X/L>>X/D.

FIG. 6 is a conceptual example configuration 600 of the mount 100 withthe linking plate 195 affixed across the sensor mounting arms 154 and175 and the restraining bolt not present. In the example configuration600, as the pipe (not shown) expands within the mount 100, the linkingplate 195 partly constrains movement of the radially distal ends 510,causing the radially proximal portions 520 of the sensor mounting arms154 and 175 to move from their substantially unstressed or pre-stressedconfiguration, as depicted in dotted lines, relatively apart to thestressed configuration depicted in solid lines. In general, with thelinking plate 195 in place, the radially proximal portion 520 of thesensor mounting arms 154 and 175 will move relatively further apart fromeach other than will more radially distal ends 510 of the sensor arms154 and 175. When the linking plate 195 is used, the pipe diameterexpansion, which can be expressed as dD=X, can result in a minimal topgap increase Xmin at ends of sensor mounting arms 154 and 175 near thelinking plate whereas Xmin is close to zero with additional andrelatively larger Xmax increase in distance between arms at locationcloser to the pipe whereas Xmax can be approximated as Xmax=˜PI*X.

Referring again to FIG. 1, in some implementations, a pivot pin (notshown) can be inserted through the bores 148, 168 of the sensor mountingarms 154 and 175. By placing the pivot pin in the bores 148, 168, as thepipe expands and contracts, the divergence of the sensor mounting arms154 and 175 will pivot about the pivot pin. For example, as the pipeexpands, the sensor mounting arms 154 and 175 can be caused to divergefrom their substantially parallel, unstressed configuration and the armswill move inwardly at an angle toward each other.

In some embodiments, the pivot pin can be compressible or otherwisedeformable, or can include a compressible or otherwise deformablecoating about a substantially non-compressible core rod. In someimplementations, the use of selected compressible or deformablecomponents for the pivot pin can provide selectable modification ofconvergence or divergence of the sensor mounting arms 154 and 175. Forexample, by including a compressible pivot pin in the pivot pinassemblies 152, 172, separation of the pivot pin assemblies 152, 172 canbe permitted in a reduced manner relative to movement that may occurwith or without the use of a non-deformable pivot pin.

In some embodiments, the linking plate 195 can be formed to have aselected spring coefficient. For example, the stiffness of the linkingplate 195 can be selected to selectably modify the divergence of thesensor mounting arms 154 and 175 under various stress configurations. Insome embodiments, one or more sensors can be mounted on the linkingplate 195. For example, sensors can be configured to provide signalsthat indicate tensile, compressive, or bending stresses at the linkingplate 195. In some embodiments, one or more sensors can be mountedbetween inner surfaces of the sensor mounting arms 154 and 175 and/or inany other suitable section of 120, 140, and/or 160. For example, a loadcell can be mounted between the sensor mounting arms 154 and 175 toprovide a signal in response to relative inward and outward movements ofthe sensor mounting arms 154 and 175.

While the present example is shown and described as including four setsof the adjustment assemblies 184, various implementations can includeany appropriate number of the adjustment assemblies 184 mounted throughcorresponding ones of the adjustment openings 181. For example, one ofthe adjustment assemblies 184 can be mounted on the upper flexingsection 140, and another one of the adjustment assemblies 184 can bemounted in the adjustment opening 181 located in the bottom flexingsection 120 approximately 180 degrees away. In another example, one ofthe adjustment assemblies 184 can be mounted in each of the upperflexing sections 140, 160, and a third one of the adjustment assemblies184 can be mounted in the adjustment opening 181 located in the centralsection of the subsection 130.

FIGS. 2 and 3 are exploded and perspective views of another exampleoptical sensor mount 200. In general, the mount 200 is removably orpermanently affixed to a pipe 201 to mechanically transmit variations inthe diameter of the pipe 201 to a collection of sensors 202, such as astrain gauges, optical sensors, Fiber-Bragg gratings, Fabry-Pérotinterferometers, or any other appropriate sensors.

The mount 200 includes a pair of mounting blocks 210 each having aproximal surface 212 and a distal surface 214. The proximal surfaces 212are positionable adjacent to an outer surface 203 of a wall 204 of thepipe 201, and spaced about 180 degrees apart from each other.

The mount 200 includes a pair of sensor mounting arms 220. One of thesensor mounting arms 220 is removably affixed to each of the distalsurfaces 214 by a collection of fasteners 222, such as bolts, screws, orother appropriate connectors. The sensor mounting arms 220 each includesa receptacle 224 configured to receive and retain an end 232 of a stemrod 230. The ends 232 are further retained by fasteners 231, such asnuts, retaining pins, or other appropriate connectors. In someembodiments, the ends 232 and the fasteners 231 can form a tensionadjustment mechanism for the stem rod 230. For example, the adjustmentmechanism can include male threads on at least one of the ends 232 ofthe stem rod 230, and the fasteners 231 can include female threadsadapted to engage the male threads of the stem rod 230. In suchexamples, the fasteners 231 can be threaded along the ends 232 to adjustthe tension along the stem rod 230.

The stem rod 230 includes at least one longitudinal receptacle 234 in anouter surface of the stem rod 230. Each of the longitudinal receptacles234 is formed to receive and retain one of the sensors 202. The stem rod230 has a first cross sectional area 236 at a central portion of one ofthe longitudinal receptacles 234, and a second cross sectional area 238at a central portion of another one of the longitudinal receptacles 234.As discussed later herein, the cross sectional areas may be the same ordifferent.

In some implementations, a magnet 240 is located in a receptacle 242formed in each of the proximal surface 212 of the mounting blocks 210.The magnets 240 include a first surface 244 positionable adjacent to theouter surface 203 of the wall 204 of the pipe 201, and a surface 246positionable adjacent to the mounting blocks 210. In some embodiments,the mount 200 can be mounted to the pipe 201 by the magnets 240. In someembodiments, the mount 200 can be mounted to the pipe 201 by welding,gluing, or otherwise adhering the mounting blocks 210 to the pipe 201.

The mount 200 is assembled in a predetermined strain condition in whichthe sensor mounting arms 200 are generally parallel to each other andthe stem rod 230 is mounted generally perpendicular to a longitudinalaxis of each of the sensor mounting arms 220. The pressure of fluidflowing through the pipe 201 exerts pressure on the wall 204, causingvariations in the diameter of the outer surface 203. As the diameterchanges, the distance between the mounting blocks 210 changes as well.Since the mounting blocks 210 are connected to each other though thesensor mounting arms 220 and across the stem rod 230, as the pipe 201expands and contracts the stem rod 230 is caused to expand or contractand/or flex. The sensors 202, mounted in the receptacles 234, are causedto expand or contract and/or flex along with the stem rod 230 andprovide signals that vary as a function of the flexure and thecompressive or tensile stress in the rod.

In some embodiments, the first cross sectional area 236 can have adifferent cross sectional area than the second cross sectional area 238.In such embodiments, the first cross sectional area 236 will expand orcontract or flex at a different rate than the second cross sectionalarea 238 relative to the expansion and contraction of the pipe 201, andthe differing rates of expansion or contraction and flexure can producediffering amounts of stress among the sensors 202. In someimplementations, the differing amounts of stress in the sensors canproduce a differential signal that can be processed to determine theabsolute or changes in fluid pressure within the pipe. In someimplementations, the thicknesses of the stem rod 230, the first crosssectional area 236, and the second cross sectional area 238 can beformed to selectively determine the amount compression, tension orflexure that occurs along the stem rod 230, and/or between the sensors202.

Although a few implementations have been described in detail above,other modifications are possible. For example, logic flows do notrequire the particular order described, or sequential order, to achievedesirable results. In addition, other steps may be provided, or stepsmay be eliminated, from the described flows, and other components may beadded to, or removed from, the described systems. Accordingly, otherimplementations are within the scope of the following claims.

What is claimed is:
 1. A method of mounting a strain sensor to a pipecomprising: positioning a mechanical clamp circumferentially around anouter surface of a pipe wall, said mechanical clamp having a centrallongitudinal axis, said mechanical clamp having a plurality of sectionsincluding: a bottom flexing section having an arcuate portionterminating at a first terminal end in a first mounting wing and saidbottom flexing section terminating at a second end in a second mountingwing, each of said mounting wings including an opening through the wingfor receiving a removable connector; a first upper flexing sectionhaving an arcuate portion terminating at a first terminal end in a firstmounting wing and said first upper flexing section terminating at secondterminal end in a pivot pin assembly having a bore parallel to thecentral longitudinal axis of the clamp, the mounting wing having anopening through the wing for receiving a removable connector; a secondupper flexing section having an arcuate portion terminating at a firstterminal end in a first mounting wing and said first upper flexingsection terminating at second terminal end in a pivot pin assemblyhaving a bore parallel to the central longitudinal axis of the clamp,the mounting wing having an opening through the wing for receiving aremovable connector; a first sensor mounting arm disposed outwardly onthe first upper flexing section, said sensor mounting arm including atleast one receptacle sized to receive and retain a first end of a firststrain gauge; and a second sensor mounting arm disposed outwardly on thesecond upper flexing section, wherein when the mechanical, said sensormounting arm including at least one receptacle sized to receive andretain a second end of a first strain gauge; and positioning a strainsensor with a first end in the receptacle of the first sensor mountingarm and a second end of the strain sensor in the receptacle of thesecond sensor mounting arm.
 2. The method of claim 1 further comprising:inserting one or more individual adjustment rods inwardly in a radialdirection toward the longitudinal axis in one or more radial openings inone or more of the bottom flexing section, the first upper flexing, andthe second upper flexing section; and contacting the outer surface ofthe pipe with a landing pad affixed to an end of each adjustment rodpositioned toward the longitudinal axis of the pipe.
 3. The method ofclaim 1 further comprising: positioning the first sensor mounting armparallel to the second sensor mounting arm when the clamp is in anunstressed condition.
 4. The method of claim 1 further comprising:positioning a second strain sensor with a first end in a secondreceptacle of the first sensor mounting arm and a second end of thesecond strain sensor in a second receptacle of the second sensormounting arm.
 5. The method of claim 1 further including connecting arigid linking plate to a distal end of the first mounting arm and to adistal end of the second mounting arm.
 6. The method of claim 1, whereinthe pivot pin includes a compressible coating thereby providingadditional flexibility to the mechanical clamp.
 7. The mounting systemof claim 2, wherein each of the landing pads include a compression padhaving at least one layer of vibration and acoustic noise absorbingmaterial affixed to each of the landing pads; and the method furtherincludes dampening vibration and acoustic noise from the pipe.
 8. Asystem for mounting strain gauges on a tubular pipe, the systemcomprising: a first mounting block having a proximal first surfacepositionable adjacent to a first portion of an outer surface of a wallof the pipe, said first mounting block having a distal mounting surface;a second mounting block having a proximal first surface positionableadjacent to second portion of an outer surface of a wall of the pipe,said second portion of the pipe wall being displaced from the firstportion, said second mounting block having a distal mounting surface; afirst sensor mounting arm connected to the distal mounting surface ofthe first mounting block, said sensor mounting arm including at leastone receptacle configured to receive and retain a first end of a stemrod; a second sensor mounting arm connected to the distal mountingsurface of the second mounting block, said sensor mounting arm includingat least one receptacle configured to receive and retain a second end ofthe stem rod; and wherein the stem rod includes a first longitudinalreceptacle in an outer surface of the rod, said first receptacleconfigured to receive and retain a first strain gauge.
 9. The mechanicalmounting system of claim 8, the stem rod having a first cross sectionalarea at a central portion of the first longitudinal receptacle andwherein the stem rod includes a second longitudinal receptacle in theouter surface of the stem rod, said first receptacle configured toreceive and retain a second strain gauge, said stem rod having a secondcross sectional area at a central portion of the second longitudinalreceptacle.
 10. The mounting system of claim 8, wherein when themechanical clamp is assembled in a predetermined strain condition thefirst sensor mounting arm is generally parallel to the second sensormounting arm and the stem rod is mounted perpendicular to a longitudinalaxis of each mounting arm.
 11. The mounting system of claim 8 furthercomprising: a first magnet received in a receptacle of the first surfaceof the first mounting block, said magnet having at least a first surfacepositionable adjacent to a first portion of the outer surface of thewall of the pipe and at least a second surface positionable adjacent tothe first mounting block; and a second magnet received in a receptacleof the first surface of the second mounting block, said magnet having atleast a first surface positionable adjacent to a second portion of theouter surface of the wall of the pipe and at least a second surfacepositionable adjacent to the second mounting block.
 12. The mountingsystem of claim 8, wherein the strain gauge is a Fiber-Bragg grating.13. The mounting system of claim 8, wherein the strain gauge is aFabry-Pérot interferometer.
 14. The mounting system of claim 8 furtherincluding a tension adjustment mechanism for the stem rod.
 15. A methodof mounting a strain gauge to a pipe comprising: positioning a firstmounting block having a proximal first surface adjacent to a firstportion of an outer surface of a wall of the pipe, said first mountingblock having a distal mounting surface; positioning a second mountingblock having a proximal first surface adjacent to second portion of anouter surface of a wall of the pipe, said second portion of the pipewall being displaced from the first portion, said second mounting blockhaving a distal mounting surface; connecting a first sensor mounting armto the distal mounting surface of the first mounting block; connecting asecond sensor mounting arm to the distal mounting surface of the secondmounting block; connecting a first end of a stem rod to the first sensormounting arm; connecting a second end of a stem rod to the second sensormounting arm; positioning a first strain gauge in a first longitudinalreceptacle in an outer surface of the stem rod, said stem rod having afirst cross sectional area at a central portion of the firstlongitudinal receptacle.
 16. The method of claim 15 further includingadjusting the tension in the stem rod prior to taking measurement withthe strain gauges using a tension adjustment mechanism on the stem rod.17. The method of claim 15 further comprising: removably securing thefirst mounting arm to the pipe by positioning a first magnet in areceptacle of the first surface of the first mounting block andpositioning the magnet with a first surface adjacent to a first portionof the outer surface of the wall of the pipe and at least a secondsurface adjacent to the first mounting block; and removably securing thesecond mounting arm to the pipe by positioning a second magnet in areceptacle of the first surface of the second mounting block andpositioning the magnet with a first surface adjacent to a second portionof the outer surface of the wall of the pipe and at least a secondsurface adjacent to the second mounting block.